Sr-89 Rx - Calibration Note

["Mike Bohan" <mike.bohan@yale.edu>]

Seasons Greetings MedPhys and RadSafers:

I haven't had a chance to fully evaluate this yet, but I thought it important
enough to give you Med. Physicists and Med. HP's out there, a heads up on
this.

We performed our first Sr-89 therapy in Sept. '93.  When the first dose came
in we assayed it in our dose calibrator (Capintec) and came up with a
correction factor (Pot Setting 683 --- Display Reading * 100) for a 5 ml
syringe.  We have been using these factors since that day to check the assay
before administration.

A couple of months ago, during an audit of our Nuclear Medicine facility, I
recommended that they purchase a new set of dose calibrator well liners and
dippers.  (They had dropped the moly assay shields more than once too often!) 


Last week, I was in the Nuc. Med. Clinic and one of our authorized users told
me that our Sr-89 calibration seemed to be off a bit from the manufacturers
stated calibration.  I went into the hot lab to check on the problem and found
that the new dipper had arrived and that it was a new design, which WILL
AFFECT your Sr-89 calibration factors!.  

The old dipper design held the handle, syringe support, and cup together with
a Plexiglas rod.  The new design incorporates the handle into a molded
semi-circular ~180 degree Plexiglas half tube which attaches to the syringe
support and bottom cup.  

While the new design should prove to be more robust, it also will absorb a lot
more of the Sr-89 betas, modifying their bremstrallung production and result
in a different calibration.

I haven't had the opportunity to recalibrate our dose calibrator yet with the
new dipper design, but I've already put it on my short list of New Year's
resolutions! (Or whenever we get our next Sr-89 dose!)

So, this is my Christmas gift to you.  Use it wisely and have a MERRY
CHRISTMAS and a HAPPY NEW YEAR!!!

Ho! Ho! Ho!

Mike Bohan
Radiation Safety Officer
Yale-New Haven Hospital
Radiological Physics
20 York St. - WWW 204
New Haven, CT   06504
mike.bohan@yale.edu
TEL (203)785-2950
FAX (203)737-4252

Since it's Christmas, I guess my employer will let me say this without the
usual disclaimer message!